Conventionally, scanning acoustic microscopy (SAM) systems have been used to find delamination areas in chip packages. For example, a SAM system may scan a sampled batch of chips to determine whether any chips have areas of delamination between layers. An area of delamination is defined as a significant gap or separation between layers of a device under test (DUT). If delamination is discovered, then a chip or batch of chips may then be categorized as faulty and subsequently discarded.
Conventional SAM systems are used to determine imperfections/delaminations between layers of devices. These properties can subsequently be analyzed. A conventional SAM system will now be described in more detail in FIG. 1.
FIG. 1 illustrates a conventional SAM system 100.
As shown in the figure, conventional SAM system 100 includes an ultrasonic transducer 102, an acoustic conductive bath 104, a detector 106 and a DUT 108. DUT 108 includes an encapsulating shell 118, an inner layer 120 and a delamination 122. Encapsulating shell 118 has a top surface 124 and a bottom surface 126. Inner layer 120 has a top surface 128 and a bottom surface 130.
In SAM system 100, acoustic conductive bath 104 is filled with water and DUT 108 is submerged in acoustic conductive bath 104.
Ultrasonic transducer 102 is placed on the surface of acoustic conductive bath 104 and transmits ultrasonic waves to DUT 108. Some of these ultrasonic waves will penetrate an interface from one media to another and some of the ultrasonic waves will transmit into and through the interface. For example, some ultrasonic waves will reflect off of the various layers within DUT 108 and some ultrasonic waves will transmit through the various layers within DUT 108.
Detector 106 is placed beneath DUT 108 and is used to measure the information gathered from a transmissive ultrasonic wave 116. Similarly, ultrasonic transducer 102 measures the information gathered from reflective ultrasonic waves 111, 113 and 115.
As a result of this ultrasonic scanning process, through transmitting ultrasonic waves 110, 112 and 114 and receiving ultrasonic waves 113 and 115, the degree of separation between bottom surface 126 and top surface 128 can be determined. This degree of separation equates to various imperfections/delaminations between encapsulating shell 118 and inner layer 120. For example, delamination 122 is one such separation between the two adjacent layers.
In some cases, if the delaminations are smaller than the wavelength of the ultrasonic wave produced by the conventional SAM system scans, the delamination will not be detected. The frequencies of the ultrasonic waves may be increased in order to increase the resolution of a scan, thus detecting smaller delaminations. However, these frequency increases require much more power. Detecting small delaminations is important because if they are not detected, small delaminations may grow larger. This may not be detected until after the DUT is in use. The DUT may then fail.
Conventional SAM systems scan devices using transmissive and reflective ultrasonic waves, and then detect interfaces in the layers of a DUT using these ultrasonic waves. An example image from a conventional SAM system scan will now be described in more detail in FIG. 2.
FIG. 2 illustrates a planar view 200 from a conventional SAM system. As shown in the figure, planar view 200 includes a DUT 202. DUT 202 includes a delamination 204, a delamination 206 and a delamination 208.
As a result of the scan from the SAM system, delaminations 204, 206 and 208 are distinguishable from other areas in DUT 202. Therefore, DUT 202 is categorized as a faulty device. If it is determined that enough DUTs are faulty within a batch of manufactured devices, then the whole batch may be discarded. Alternatively, if it is determined that enough DUTs within a batch pass the scanning process and are not faulty, then the whole batch may be used.
Conventional SAM systems may detect some areas of delamination in a DUT. In some instances conventional SAM systems may not detect areas of delamination, but the DUT may fail when it is in use. This failure may be caused by undetected delaminations in the DUT, for example because the delaminations were smaller than the resolution of the SAM during the testing phase, but enlarged when the DUT was actually used What is needed is a system and method that increases the likelihood of detecting areas of delamination for a DUT and provides a way to determine other substantive properties of the device.